Alternating current protective relay



Aug. 16, 1932.

F. OLLENDORFF ET AL 1,871,822

ALTERNATING CURRENT PROTECTIVE RELAY Filed Aug. 30, 1929 VVV INVENTOR 3/Franz Ol/endorf Er/ch Fr/ed/d'nc/er 7 AT'TORNEY Patented Aug. 16, 1932UNITED STATES PATENT OFFICE FRANZ OILENDORFF, F BERLIN-WILMERSDORF, ANDERICH FRIEDLANDER,-OF SPAN DAU, NEAR BERLIN, GERMANY, ASSIGNORS TOWESTINGHOUSE ELECTRIC & MANU- FACTURING COMPANY, A CORPORATION OFPENNSYLVANIA ALTRNATING CURRENT PROTECTIVE RELAY Application filedAugust 30, 1929, Serial No. 889,871, and in Germany September 22, 1928.

This invention relates to relay protective means for A. C. machinesandA. C. systems. Heretofore relay schemes for over-current protection,differential protection, phase balancing and other known functions, havebeen controlled by any one of the A. C. quantities to be supervised. Itis a recognized fact that it is not advisable to provide protectivemeans for networks and the like which are responsive to all operativeconditions of such systems for the same strength of the quantity to besupervised. For example, the same value of current may arise in an A. C.machine at a low value of the exciting current, in which case adisturbed operation would be the cause,

or the machine may be operating with the same value of current but witha higher exciting current in which case the machine would be operatingunder normal conditions.

However, the relay cannot take these conditions into consideration andwill always respond at the same current.

According to this invention, therefore, the sensitiveness of the relayis dependent upon the exciting current of the A. C. machine, and in sucha manner that the sensitivity is diminished by increasing excitationcurrent, so that, with stronger excitation of the A. C. machine, itresponds later than withweak excitation.

An object of this invention, therefore, is to provide a protective relaythe sensitivity of which is proportional to the exciting current of anA. C. machine with which it is associated.

gized therefrom and a pivoted armature 13 in rotatable relation withrespect thereto. The series connected coils 14 of the electro magnettend to pull the armature 13 from its normally biased position, asshown, into a horizontal position, thereby closing the contacts 15 bythe movement of the contact arm 16, which is substantially a portion ofthe armature 13. The biasing or damping efiect on the'armature 13 isobtained by means of the spring 17, one end of which is connected to thearmature 13 and the other end to an iron core 18 which is magnetized bythe coil 19.. The coil 19 is adapted to be energized from the exciter,not shown, or the excitation current of the A. C. machine 11. Thismagnetizing action of the coil 19 causes a tension or pull on the spring17 in direct proportion to the amount of excitation current. The

armature will, therefore be moved to close thecontacts 15 on theoccurrence of an unbalance in the system for any degree of excitation.

In the arrangement shown in Fi 2, a three phase star-connected A. C. macine 21 is adapted to be controlled in the event of a disturbancetherein, in proportion to its degree of excitation. A circuit comprisinga three phase auxiliary choke coil 23 and the primary of a currenttransformer 24 is interposed between the star connection of the A. C.machine 21 and its output circuit 22.

A dynamometer type relay 25 is interposed in the secondary circuit ofthe transformer 24 and is adapted to cause the disconnection of the A.C. machine by suitable switching means, not shown. On the occurrence ofan unbalance between the phases of the circuit 22, a resultant currentwill flow through the transformer 24 and energize the windings of therelay 25. The sensitiveness of the relay is adapted to be dependent onthe current in the exciting winding 26 of the A. C. machine by means ofa resistance 27 which is inserted in that part of the exciter circuitwhich includes the Winding 26. The

voltage drop across the resistance 27 is impressed on the windings ofthe relay 25 in such a manner that the portion of the D. C. excitingcurrent taken from the resistance 27 tends to flow in a directionopposite to that of the current from the transformer 24. The two coilsof the relay 25 are in series in the secondary circuit of thetransformer but are in parallel with respect to the applied D. C.exciting current. This result is obtained by providing an inductance 28connected in parallel to the relay and having a central tap to which oneof the D. C. conductors is connected. A blocking condenser 29 is provided to prevent the D. G. current from flowing into the circuit of thetransformer 24. If the inductances and resistances of the relay arearranged symmetrically, an ordinary Wheatstone bridge results, and theblocking condenser 29 is not necessary.

yThe above arrangement produces a sensitivity of the relay whichdiminishes with increasing energization, the degree of the sensitivitybeing greater the smaller the degree of excitation. Without thedirective force of the exciting current, the sensitivity of the relay isdirectly proportional to the energizing current. The proportionalityfactor can be controlled by selecting the distribution ratio between therelay direct-current and energizing current.

In Fig. 3 is shown a three phase A. C. machine 31 energized by anexciter 32 having a field winding 33 therefor, a current transformer 34in one of the phases of the output circuit 35, of the said machine,adapted to energize the coil 36 of the relay 37 on the occurrence of anovercurrent. A choke coil 38 has one of its three legs energized by adirect current proportional to the exciting current, as from the D. C.source 39 through the winding 33 and the variable resistance 41. Theother two legs of the choke coil are connected in series and paralleledwith the coil 36 of the relay 37.

The energizing coil of the relay 37 and the series windings of the chokecoil 38 are therefore energized in a proportionate amount determined bythe amount of current flowing in the circuit 35 of the machine 31. Withan increase of excitation current of the machine 31, the inductance ofthe choke coil 38 is diminished in increasing degree by the D. C.magnetization, so that the current delivered by the current transformer34 flows for the greater part through the choke coil 38, and the currentwhich flows through the energizing coil of the relay 37 isproportionately smaller. This distribution of the current in theparallel circuit, including the relay 37 and the choke coil 38, results"n a degree of sensitivity of the relay proportional to the relationbetween the exciting current and the outjput current of the A. C.machine.

In the oregoing arrangement, a usual type of relay may be used toactuate a control or protective system and the reaction of the A. C.current on the D. 0. current is avoided.

This invention as applied to the protection of A. 0. systems is notconfined to the various arrangements shown in the drawing, and nolimitations should be placed thereon other than those set forth in theappended claims.

We claim as our invention:

1. In combination with an alternatingcurrent machine, current-responsivemeans associated therewith and energized in accordance with the machinecurrent, and means energized in accordance with the exciting current ofsaid machine for Varying the sensitivity of said current-responsivemeans.

2. In combination with an alternatingcurrent machine, acurrent-responsive means associated therewith and energized inaccordance with the machine current, and means energized in accordancewith the exciting current of said machine for controlling thesensitivity of said current-responsive means.

3. A current-responsive device associated with an alternating-currentcircuit and responsive to the circuit current, and means energized inaccordance with the circuit excitation current for varying thesensitivity of said device.

4. Protective means for an alternating currrent system including incombination a current-responsive device associated with said system andadapted to be energized in accordance with the current in said systemand means energized in accordance with the system exciting current forpredetermining the sensitivity of said device.

5. In a protective system for an alternating-current circuit, acurrent-responsive means associated therewith and responsive to thecurrent thereof and means associated with the excitation circuit of saidalternating-current circuit and with said current-re,

sponsive means for modifying the response of said protective system.

6. Protective means for an alternatingcurrent system, including acurrent-responsive relay energized therefrom in accordance with thecurrent thereof, and damping means associated with the excitationcircuit of said system and with said relay for varying the sensitivityof said relay inversely as the value of the exciting current.

7. A protective system for an alternatingcurrent machine connected in anelectrical circuit, comprising a current-responsive relay, means forenergizing said relay in accordance with the current traversing saidcircuit, and means associated with the excitation circuit of saidmachine for predetermining the sensitivity of said relay in accordancewith the degree of excitation of said machine.

8.'Protective means 'for an alternatingcurrent electric circuitincluding a current relay associated with said circuit and adapted to beenergized in accordance with the circuit current, and means energized inaccordance with the circuit excitation current for biasing said relay.

In testimony whereof, we have hereunto subscribed our names atBerlin-Siemensstadt, Germany, this 16th day of July, 1929. Q FRANZOLLENDORFF.

ERICH FRIEDLKNDER.

